The present invention relates to a driving force distribution control device that controls driving force to be distributed to an auxiliary drive wheel, and relates to a four-wheel-drive vehicle.
In the related art, there has been a driving force distribution control device which distributes driving force to an auxiliary drive wheel at a predetermined rate at which an abnormal vibration is not generated when a driving state of the four-wheel-drive vehicle is in an abnormal vibration generation region in which an abnormal sound due to the abnormal vibration caused by knocking of the engine is generated in a driving force transmission system (for example, Patent Document 1).
The driving force distribution control device disclosed in Patent Document 1 is configured so as to generate frictional torque suitable for mitigating the abnormal sound in a torque coupling when a vehicle speed exceeds a vibration generation lower limit speed and is less than a vibration generation upper limit speed. The frictional torque has a value higher than that in a case where the vehicle speed is not in the abnormal vibration generation region.
(Patent Document 1) JP-A-2001-277881
However, the abnormal sound from the driving force transmitting system is not limited to that caused by knocking, and can also be generated by pulsation (cyclic fluctuation) of torque of the engine. Furthermore, in order to improve fuel efficiency, when there is a small need to transmit driving force to the auxiliary drive wheel, for example, as in a straight constant speed running, it is desirable to reduce the driving force to be transmitted to the auxiliary drive wheel as far as possible to reduce the frictional torque in the driving force transmitting system. Thus, the present inventors have earnestly persisted in their research, focused on the fact that the engine torque is related to presence or absence of the generation of the abnormal sound, and found that, even if the number of revolutions of the engine is in a range in which the abnormal sound can be generated, the abnormal sound does not occur depending on a value of the engine torque and the driving force to be transmitted to the auxiliary drive wheel can be reduced in such a state.